There are in existence devices for charging and recharging various types and sizes of storage batteries including the larger wetcell type batteries as well as smaller drycell batteries such as nickel-cadmum (Ni-Cd) battery cells and the like. The present invention is directed primarily to those chargers used for charging dry cell batteries such as Ni-Cd and related type batteries sometimes also referred to by and including designations such as AA, AAA, C, D, and 9 V batteries.
Known commercial chargers for these types of batteries or cells fall into two general catagories, namely the trickle chargers and so called one hour chargers. The trickle chargers generally provide a partially regulated charge rate, typically in the range of 15-150 milliAmperes (ma) of charging current. Such chargers do not ordinarily include means to protect against reverse charging voltages or against overcharging, and such devices are slow to charge usually requiring charging periods in the range of 14 hours and longer for charging a battery such as a C battery. This will vary somewhat for other cells and other charging rates.
The one hour chargers, on the other hand, are designed mainly for charging cell packs such as portable tool cell packs often included in tools such as power drills and the like. The power packs used in such devices are multi-cell packs with the individual cells connected in series to produce a voltage output that is greater than the output of the individual cells. Such cell packs may have built into them thermostatic sensing devices which operate to terminate a charging operation if the battery temperature exceeds some predetermined amount.
No known device, however, has means for individually and selectively fast or trickle charging one or more cells independently of others and wherein certain conditions of each cell are monitored and used to control means to determine the charge rate to be used and/or if a particular cell is to be charged at all. Furthermore, no known battery charger device includes means for making calculations and determinations as to certain conditions of each of a plurality of batteries being charged in order to control whether to fast or trickle charge, or to terminate a charging operation under certain conditions or determine whether a particular battery can accept a fast or only a trickle charge. Still further, no known battery charger includes a microprocessor capable of responding to certain parameters individually as to a plurality of batteries connected to be independently charged and using such information to make calculations and determinations which control if and how a battery is to be charged, and no known battery charger has means under control of a microprocessor for individually indicating for each battery being charged the type of charging it is undergoing. Also no known battery charger senses the difference between the battery voltage during a charging (closed circuit voltage--CCV) operation and the battery voltage when the battery is not being charged (open circuit voltage--OCV) and processes differences to terminate a charging operation when the actual value of this process result exceeds the minimum value of this difference during a charging operation by some predetermined difference usually espressed as a ratio. Also no known battery charger has means to terminate a charging operation such as if the open circuit voltage (OCV) exceeds some predetermined value, or if the condition of the open circuit voltage changes in some predetermined manner, if the closed circuit voltage exceeds some predetermined threshold value, if the charging cycle times out, i.e. exceeds some predeterminted charging time, such as 60 minutes or if the ambient temperature exceeds or is less than some predetermined temperature.
No known battery charger calculates a divergence between open and closed circuit voltages of a battery being charged and includes means for retaining the minimum value thereof during a charging operation for comparison with the instantaneous value of the same voltage difference to determine when the ratio therebetween is such that a charging operation should be terminated.
It is a principal object of the present invention to provide a battery charger device that includes means that can make a determination as to whether a battery or cell to be charged can be subjected to a fast charge to reduce the required charging time or must be more slowly trickle charged or not charged at all.
Another object is to provide means sensitive to ambient temperature and/or cell voltage for determining if a battery or cell can be subjected to a fast charge condition.
Another object is to provide a battery charger device that includes means capable of individually evaluating a plurality of batteries or cells of the same or of different kinds and with the same or different existing charge levels to be charged to determine which can be fast charged and which can not and proceeding to charge them accordingly.
Another object is to provide a battery charger device having means capable of individually monitoring selected conditions of one or more batteries during charging thereof.
Another object is to sense battery voltage during on-charge (closed circuit) and off-charge (open circuit) times, using the difference between these voltages for each individual battery or cell over the charging cycle to determine when to terminate charging.
Another object is to provide a battery charger device that is safe to use and very unlikely to damage batteries being charged thereby.
Another object is to provide an improved microprocessor controlled battery charger.
Another object is to provide improved software for controlling a battery charger device.
Another object is to miminize the time required to charge batteries.
Another object is to provide a battery charger with means to terminate a charging operation for a battery when the ambient temperature is less than or exceeds some predetermined temperature.
Another object is to provide a microprocessor controlled visual display that indicates the individual charge status of a plurality of batteries or cells connected thereto to be charged.
Another object is to use open circuit and closed circuit battery voltages during a charging operation to determine some of the conditions that can be used to terminate a charging operation.
Another object is to terminate a battery charging operation after the lapse of some predetermined charging time interval.
Another object is to terminate a battery charging operation if the rate of change of the battery voltage exceeds some minimum amount.
Another object is to provide a wide range of detectable conditions that can be used to terminate a battery charging operation.
Another object is to teach the construction and operation of a battery charging device which is more versatile and safer to use from the standpoint of the batteries being charged than any known device used for the same or similar purposes.
Another object is to terminate a battery charging operation based on a predetermined change in the condition of the open circuit voltage.
These and other objects and advantages will become apparent after considering the following detailed specification of a preferred embodiment of the subject device in conjunction with the accompanying drawings.